Embodiments of this invention are directed to a highwall mining arrangement in which a plurality of conveyor cars are linked together in series to form a conveyor train led by a mechanical miner. The miner and train of conveyor cars progresses into a seam (e.g., an elongate hole) that is created or mined into a vertical wall of a hillside. The miner loosens and extracts coal, or some other mineable material. The conveyor cars then pass the material along the train and out of the seam where the material may be collected and hauled away.
Highwall mining systems are known to efficiently mine near surface coal from seams with a low excavation cost, high yield, and low level of environmental damage. In highwall mining methods, the surface of the hillside is vertically excavated to the vertical level of the coal seam as is the case with a conventional surface mine. A vehicle, which may be referred to as a “launch vehicle”, is placed near or adjacent to the exposed vertical wall of the seam. A mobile mining machine, referred to as a “miner”, is launched into the exposed face of the seam. As the miner progresses in loosening and removing the coal from the seam, it forms an elongate hole that may be up to, for example, about eleven and one-half feet in width (as determined by the width of the miner's cutter drum) and up to about sixteen feet in height (as determined by the height of the layer of coal or other material being mined). Using a miner of this size, it is possible to mine seams of up to twenty-eight feet in height when the mining is performed separately for an upper section and a lower section of the seam. Smaller miners may be used with smaller seams of mineable material. In some embodiments, the hole may extend to over 2000 feet in length.
The miner used in highwall mining may be the same as is used in traditional underground coal mines. The miner may include a cutter apparatus which moves up and down the face of the coal seam, loosening and extracting coal in a perpendicular direction away from the face. The conveyor cars carry the extracted coal from the miner to the launch vehicle. Propulsion cylinders in the launch vehicle may guide the mining apparatus into the coal seam. These propulsion cylinders may also withdraw the mining apparatus out of the seam after the mining of the coal has been completed. As the mining arrangement advances into the seam, conveyor cars are sequentially added to the back of the train. These conveyor cars transfer the coal back from the miner to the launch vehicle on conveyor belts. From the launch vehicle, the coal may be collected and carried away by dump trucks for off-site processing.
One advantage of highwall mining is that there is no need for people to enter the coal seam, which may be a hazardous environment, as is well known. Because no people are physically at risk, the mining operation may be conducted without any roof support. One or more cameras in the area of the miner may be used to produce video images of the mining operation, and these video images may be viewed in real time by the operator of the launch vehicle. One or more cables or chains may extend from the launch vehicle to the conveyor cars and the miner while the miner is in operation. These cables or chains may be used to assist in advancing the train into the seam, or pulling the train out of the seam, as required.
A problem is that none of the currently available highwall mining systems are efficient and practical in mining seams having relatively steep slopes, e.g., slopes over about 15 degrees. The existing prior art systems are also, in general, relatively cumbersome to move from one location to another. Often, relocation requires substantial dismantling of these complex systems over a time span of several days. U.S. Pat. No. 6,652,035 to Chisholm discloses the use of hydraulic cylinders for tilting and changing the elevation of an entire launch vehicle to substantially match a dip angle. Accordingly, the coal conveyor belt of the launch vehicle carries the coal at an upward angle away from the seam, allowing the force of gravity to cause some of the coal to fall backward on the conveyor belt or fall off of the conveyor belt. Moreover, when conveyor cars are loaded onto and unloaded from the launch vehicle, a front end loader must awkwardly hold the conveyor cars at the same angle at which the launch vehicle is oriented (e.g., at the dip angle). In addition to the difficulty this presents to the operator of the front end loader, there is also the risk that the conveyor car may flip over off of the front end loader when supported at such a steep angle.
In view of the known methods described above, there is a need for a highwall mining system capable of efficient and practical operation in steep dip seams, e.g., seams oriented at angles of over about 15 degrees relative to the horizontal direction.